Expression of transcription factors in MEN1-associated pancreatic neuroendocrine tumors

MEN1-associated pancreatic neuroendocrine tumors (pNETs) may potentially express distinct hormones, but the mechanism has not been elucidated. Transcription factors such as MafA and Pdx1 have been identified to lead to beta cell differentiation, while Arx and Brn4 to alpha cell differentiation in developing pancreas. We hypothesized those transcription factors are important to produce specific hormones in pNETs, similarly to developing pancreas, and examined the expression of transcription factors in a case of MEN1 who showed immunohistological coexistence of several hormone-producing pNETs including insulinoma. A 70-year-old woman was found to manifest hypoglycemia with non-suppressed insulinemia and hypercalcemia with elevated PTH level. She was diagnosed as MEN1 based on the manifestation of primary hyperparathyroidism, pituitary adenoma and insulinoma, with genetic variation of MEN1 gene. She had pylorus-preserving pancreaticoduodenectomy because CT scan and SACI test indicated that insulinoma was localized in the head of the pancreas. Histopathological finding was MEN1-associated NET, G1. Interestingly, immunohistological examination of the resected pancreas revealed that two insulinomas, a glucagon-positive NET and a multiple hormone-positive NET coexisted. Hence, we examined the expression of transcription factors immunohistochemically to elucidate the role of the transcription factors in MEN1-associated hormone-producing pNETs. We observed homogeneous expressions of MafA and Pdx1 in insulinomas and Arx in glucagon-positive NET, respectively. Moreover, multiple hormone-positive NETs expressed several transcription factors heterogeneously. Collectively, our results suggested that transcription factors could play important roles in the production of specific hormones in MEN1-associated pNETs, similar to islet differentiation

Dipeptidyl peptidase-4 inhibitor treatment induces a greater increase in plasma levels of bioactive GIP than GLP-1 in non-diabetic subjects

Objective: Glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) possess multiple bioactive isoforms that are rendered non-insulinotropic by the enzyme dipeptidyl peptidase-4 (DPP-4). Recently, some ELISA kits have been developed to specifically measure “active” GIP and GLP-1, but it is unclear if these kits can accurately quantify all bioactive forms. Therefore, it remains uncertain to what extent treatment with a DPP-4 inhibitor boosts levels of biologically active GIP and GLP-1. Thus, we evaluated our novel receptor-mediated incretin bioassays in comparison to commercially available ELISA kits using plasma samples from healthy subjects before and after DPP-4 inhibitor administration. Methods: We utilized cell lines stably co-transfected with human GIP or GLP-1 receptors and a cAMP-inducible luciferase expression construct for the bioassays and commercially available ELISA kits. Assays were tested with synthetic GIP and GLP-1 receptor agonists and plasma samples collected from subjects during a 75 g oral glucose tolerance test (OGTT) performed before or following 3-day administration of a DPP-4 inhibitor. Results: A GIP isoform GIP(1–30)NH2 increased luciferase activity similarly to GIP(1–42) in the GIP bioassay but was not detectable by either a total or active GIP ELISA kit. During an OGTT, total GIP levels measured by ELISA rapidly increased from 0 min to 15 min, subsequently reaching a peak of 59.2 ± 8.3 pmol/l at 120 min. In contrast, active GIP levels measured by the bioassay peaked at 15 min (43.4 ± 6.4 pmol/l) and then progressively diminished at all subsequent time points. Strikingly, at 15 min, active GIP levels as determined by the bioassay reached levels approximately 20-fold higher after the DPP-4 inhibitor treatment, while total and active GIP levels determined by ELISA were increased just 1.5 and 2.1-fold, respectively. In the absence of DPP-4 inhibition, total GLP-1 levels measured by ELISA gradually increased up to 90 min, reaching 23.5 ± 2.4 pmol/l, and active GLP-1 levels determined by the bioassay did not show any apparent peak. Following administration of a DPP-4 inhibitor there was an observable peak of active GLP-1 levels as determined by the bioassay at 15 min after oral glucose load, reaching 11.0 ± 0.62 pmol/l, 1.4-fold greater than levels obtained without DPP-4 inhibitor treatment. In contrast, total GLP-1 levels determined by ELISA were decreased after DPP-4 inhibitor treatment. Conclusion: Our results using bioassays indicate that there is a greater increase in plasma levels of bioactive GIP than GLP-1 in subjects treated with DPP-4 inhibitors, which may be unappreciated using conventional ELISAs. Keywords: Receptor-mediated incretin bioassays, Glucose-dependent insulinotropic polypeptide, Glucagon-like peptide-1, Dipeptidyl peptidase-

低血糖発作を繰り返す反応性低血糖症症例の2度の妊娠管理に関する報告

雑誌掲載版耐糖能異常合併妊娠では妊娠中の厳格な血糖コントロールにおいて、血糖値の目標下限値は70mg/dlとされているが、低血糖が母児へ与える影響については不明な点が多い。動物実験では妊娠初期の低血糖が胎児奇形や発育遅滞に影響するといった報告もある。今回われわれは、非妊娠時より低血糖発作を繰り返した症例で、2度の妊娠管理を経験した。症例は19歳ごろより空腹時の脱力感を自覚し、21歳で随時血糖値24mg/dlの低血糖発作を発見され、2007年1月当科紹介初診。低血糖の入院精査にて、インスリノーマや内分泌疾患などは否定し、75gブドウ糖負荷試験(OGTT)にて血糖値は0分値65mg/dl、60分値122mg/dl、120分値65mg/dlであり、インスリン値からも反応性低血糖症と診断した。αグルコシダーゼ阻害薬を開始したが、挙児希望のため内服を中止し、2007年10月(22歳)に第1子の妊娠判明。妊娠19週2日に食後血糖値66mg/dl、HbA1c 4.6%、40〜50mg/dlの低血糖発作を繰り返しており、補食や分割食で対応していた。妊娠25週5日の75g OGTTでは0分値78mg/dl、60分値154mg/dl、120分値112mg/dl。5分割食として低血糖発作を予防し、妊娠40週1日で2420g、低出生体重児でSFD(small for date)の女児を出産。25歳時には第2子の妊娠判明、HbA1c 5.4%であり、妊娠初期から5分割食を指示し、重篤な低血糖発作はなく経過。妊娠37週4日で2754g、AFD(appropriate for date)の女児を出産。母体体重は第1子妊娠中には約11kg、第2子妊娠中には約8kgの増加であった。2児ともに奇形や明らかな新生児合併症はなく、その後の発育も順調である。本症例では、胎児発育に影響を与えるその他の要因を認めず、2回の異なる妊娠経過から、妊娠中の繰り返す低血糖は児の発育遅延に関係する可能性が考えられた